Unfortunately no. And since the methods contained in these helpers are used statically, it would've been hard to override them effectively anyway. Btw, this particular helper is used in the following view classes:

ViewPublic/Conversation/View.php

ViewPublic/Conversation/ViewNewMessages.php

ViewPublic/Thread/View.php

ViewPublic/Thread/ViewNewPosts.php

ViewPublic/Thread/ViewPosts.php

...so you can try extending these classes individually to achieve the same thing.
Not ideal. But it would work.